While drilling and producing wells for the recovery of petroleum and other subsurface deposits, it is often necessary to close off or plug a tubular conduit, such as a string of tubing extending from the well surface to a subterranean location, at a chosen point along the length of the conduit. Subsequently, it is necessary to be able to re-open the conduit for flow therethrough. A plug used to close off the tubing during setting of a well tool, such as a packer, may then be released so that fluid may be circulated through the tubing.
Certain types of plugs are designed to be permanently installed, and they must be drilled or milled to be removed, which can be labor intensive. Other types of plugs are designed to be retrieved when the purpose for which the plug has been installed has been accomplished. Retrievable plugs generally employ some form of releasable anchoring device by which the plug may be secured to the internal bore of the well pipe and which may then be released to enable the plug to be withdrawn. One disadvantage of this prior art arrangement is that a restriction in the internal diameter of the tubing string often accompanies the design. Also, the prior art plugs were often retrieved on a wireline and the retrieval operation was complicated in the case of deviated well bores. Debris that sometimes accumulates on the top of the retrievable plug can also cause issues in the wellbore.
Another prior art plug design involves the incorporation of a plug of expendable material and an actuating device used to dislocate or fracture the plug upon receipt of a triggering signal. The potential for remaining and problematic debris from the plug in the tubing string or wellbore must be carefully monitored in such devices. Sand plugs, for instance, have been provided for zonal isolation within wellbores, however the integrity of such sand plugs can be inconsistent and remaining particulates must be dealt with.